Thermal ink jet pens commonly utilize heater resistors that are placed on a common substrate and are aligned with individual ink reservoirs and corresponding ink ejection nozzles. The heater resistors are electrically driven by conductive traces which are photolithographically formed on the surface of a suitable resistor material, such as tantalum-aluminum. The heater resistors are isolated from the overlying ink reservoir by an inert dielectric material.
To reduce the number of conductors required to drive the heater resistors, the prior art has combined the resistors with diodes to enable the resistors to be formed into an X-Y matrix which is, in turn, driven by a multiplexing circuit. Such an arrangement is shown in U.S. Pat. No. 4,695,853 to Hackleman et al., assigned the same Assignee as this patent application. U.S. Pat. No. 5,103,246 to Dunn, assigned to the same Assignee as this patent application, describes a technique for configuring such an X-Y electrical multiplexing arrangement so as to enable highly dense packing of the heater resistors. In each reference, a single resistor is employed per ink jet ejection nozzle.
U.S. Pat. No. 5,134,425 to Yeung, assigned to the same Assignee as this patent application, shows a further X-Y addressing matrix for plural ink jet heater resistors. Yeung describes a circuit which addresses the problem of parasitic voltages which appear across non-addressed heater resistors when plural addressed heater resistors are subjected to drive voltages. The parasitic voltages result from current flowing through non-addressed resistors along alternate paths between a drive voltage source and electrical ground. The preferred embodiment disclosed by Yeung drives each heating element in the matrix with a specified voltage and applies constant voltages across non-addressed heating elements, thus limiting the variations in total power dissipation of all heating elements. The power dissipated by each non-addressed heating element is less than or equal to 1/4 of the power that is dissipated by an addressed heating element, thus reducing the danger of misfiring in any particular print head design.
Notwithstanding the success of prior art ink jet driving apparatus and circuitry, there is a continuing demand to achieve both simplification of the driving circuitry and reduced cost. Further, there is a need to assure that whatever driving technique is utilized enables reliable operation of the ink jet pen.
Accordingly, it is an object of this invention to provide an improved apparatus for selecting and driving individual ink jet nozzles.
It is another object of this invention to provide a simple structure that enables an X-Y multiplexed drive circuitry to selectively address ink nozzles.
It is yet another object of this invention to provide an improved apparatus and method for controlling addressing of individual ink jet nozzles.